The Moon in Binoculars
The Moon is one of the most beautiful and fascinating objects to observe with a pair of binoculars. Every night a different phase of the Moon is visible, bringing new craters, seas, and mountains into view.
The Moon is also great for astronomy because you don’t have to worry about light pollution because the Moon is so bright. You will be astonished at how much you can see through a pair of binoculars – but seeing the maximum amount of detail on the Moon requires two things. Firstly, you have to hold your binoculars steadily. Even a small amount of shaking makes it difficult to examine features. Sit back in a comfortable chair with elbow support, or secure the binos on a tripod to improve the view substantially (although at the expense of some convenience). Or get your broom and place it upside down with the binoculars resting on the brush end. It really steadies things up!
Secondly, explore the strip of the Moon’s illuminated surface next to the terminator. The terminator is the boundary between light and dark. The sun is rising along this line, and so the shadows are at their maximum length. (In fact, if you watch for a few minutes, you can actually see the shadows change as the sun rises.) The angle of the sunlight most clearly reveals the topography of craters, mountains, and valleys and brings them into stark relief.
Ironically, one would think that Full Moon is the best time for viewing the Moon, but it is actually the worst time to view it if you want to see craters, mountains and interesting features on the seas. The best observing times are from shortly after New Moon until about 2 days after First Quarter in the evening sky, and from about 2 days before Last Quarter to almost New Moon in the morning sky. However, if you want to see the Moon’s incredible rays system and all its seas and highlands, then Full Moon observing is superb.
The Lunar Seas
When observing the Moon with the naked eye, the easiest things to spot are the lunar seas – the large, dark plains that show up in good contrast to the lighter highland areas. They are known as seas because ancient astronomers believed them to be real seas and named them appropriately. Individually, each “sea” is known by its Latin name, as a mare (pronounced “marr-ay”). Collectively, these seas are known as maria (“marr-ree-ah”). The most famous of the seas is Mare Tranquillitatis, the Sea of Tranquility. It’s here, on July 20th, 1969, that Apollo 11 landed and Neil Armstrong became the first man to walk on the Moon.
Today we know that they are large basaltic plains formed by volcanoes that once erupted on the very young Moon, some three to four billion years ago.
The lunar maria were named in 1651 by Giovanni Riccioli (1598-1671), an Italian Jesuit priest, astronomer, and physicist, and he named them after moods or meteorological phenomena. Mare Cognitum was unnamed and received its name in 1964 in reference to its selection as the target for the successful impact probe Ranger 7, the first American spacecraft to return closeup images of the Moon’s surface.
The seas are fascinating to explore with your binoculars – they are full of complex shades of grey (and at Full Moon, sharp-eyed observers can pick up subtle tints of colour – bluish-grey; olive-grey, yellowy-grey, brownish-grey, and reddish-orangish-grey). And it’s interesting to see the relationship between the dark lunar seas and the bright, heavily cratered highland regions.
Lunar Maria (and diameters)
1. Mare Crisium = Sea of Crises (418 km)
2. Mare Fecunditatis = Sea of Fertility (909 km)
3. Mare Nectaris = Sea of Nectar (333 km)
4. Mare Tranquilitatis = Sea of Tranquility (873 km)
5. Mare Serenitatis = Sea of Serenity (707 km)
6. Mare Frigoris = Sea of Cold (1,596 km)
7. Mare Vaporum = Sea of Vapours (245 km)
8. Mare Imbrium = Sea of Showers (1,123 km)
9. Mare Insularum = Sea of Islands (513 km)
10. Oceanus Procellarum = Ocean of Storms (2,568 km)
11. Mare Cognitum = Sea That Has Become Known (376 km)
12. Mare Nubium = Sea of Clouds (715 km)
13. Mare Humorum = Sea of Moisture (389 km)
Craters
The quintessential lunar feature is its craters – it has thousands of them, the remnants of asteroid and meteor impacts that vary in size from microscopic pits to sprawling depressions up to 350km in diameter. (Anything larger is a basin.) Impact craters are the depressions left behind after an asteroid, meteoroid, or comet collided with the Moon. Because of the Moon’s lack of water, atmosphere, and tectonic plates, there is little erosion, and the craters span a vast amount of time – from those that are billions of years old to the remarkable Tycho which is only about 108 million years old. The age of large craters is determined by the number of smaller craters contained within it, older craters generally accumulating more small, contained craters.
Riccioli named the craters for famous scientists, philosophers and explorers – a tradition that has continued today, albeit you have to dead to get a crater named after you! The only craters that have been named for living people were the Apollo 11 astronauts – Armstrong, Aldrin and Collins – whose craters lie close to the landing site on the Sea of Tranquility (but alas, too small to be seen in binoculars).
Many of the larger craters offer a great view in binoculars when observed along the terminator. And during Full Moon the face of the Moon is littered with the bright spots of craters.
Mountains
In addition to craters and seas, the moon is home to some pretty massive mountains that you can see in binoculars. Along the terminator, look for mountaintops protruding high enough to catch sunlight while dark, lower terrain surrounds them. If you look again in a day or two, they will be practically invisible except for their whiter color. The most spectacular of the lunar ranges is the beautifully curved 600km long Montes Apenninus. It forms the southeastern edge of the Imbrium Basin and you can see its peaks when it lies along the terminator.
The Full Moon Rays
Most people think that the worst time to observe the Moon is when it’s full. Not so! Quite apart from being the most beautiful globe that seems to glisten with its moonlight, you are looking at the entire half of the Moon where billions of years of Solar System impact history are preserved. Unlike Earth, the Moon’s lack of weather and plate tectonics make it a geological time capsule. The Moon’s surface tells a violent story – of the heavy bombardment roughly 4 billion years ago when the inner solar system was pummeled by asteroids and comets. The craters, the seas, the mountains, the rays… they all tell the story. It really is something to see in binoculars.
However, most incredible of all are the beautiful ray systems that are seen in their full glory at full Moon. They are dramatic, incredibly complex and absolutely fascinating. It is a mind-bender to look at the rays and try to appreciate the force behind an impacting projectile that scattered boulders, rocks and pulverized ejecta hundreds (and in some cases, thousands) of kilometres across the surface of the Moon. They are also a lesson in ballistics as you can see in which direction the impactor was flying when it whacked the Moon
The most spectacular ray system of all is Tycho’s. Its stupendous rays rocket off in a butterfly pattern toward the northwest, east, and southwest, partially encircling the full Moon, and draping themselves over all sorts of lunar features. One incredible ray extends all the way across Mare Serenitatis… and keeps on going. (You can see its amazing rays on the “seas” image. Tycho and its rays are unmistakable at the bottom half of the image.)
Unlike Tycho’s rays that fly out across the face of the Moon, Copernicus’ rich assortment of rays are short, feathery and plume-like.
Earthshine
When you look at a crescent moon shortly after sunset or before sunrise, you can sometimes see not only the bright crescent of the moon, but also the rest of the moon as a dark disk. It’s called earthshine and it is when sunlight reflected from the Earth faintly illuminates the dark portion of the Moon’s disc. Very pretty!
Lunar Eclipse
And of course the ultimate in lunar observing in binoculars is during a lunar eclipse!
Fantastic computer-based lunar atlas
You really can’t get anywhere here on Earth without consulting a map and similarly, you can’t identify much on the moon without a map either. And the best map of all is this free download of an amazing computer-based atlas of the Moon. It is designed to be easy to use and in particular “in the field” because the Moon is so bright that light pollution doesn’t affect your eyes and observation. So you can have your laptop or mobile beside you so that you can not only identify what features you are seeing, but also get all the pertinent information you could possibly want. It is a superb aid when you are cruising the Moon in your binoculars.
And a great thought to end on…
An entire lunation – from one New Moon to the next – takes a month here on Earth… but on the Moon it was simply one day!
Copyright © Susan Young 2025